Amidocarboxylic acids are desirable surfactants in that they have good water solubility, good detergency and foaming properties and are mild to skin and hair. One method for the production of such surfactant is through the oxidation of an alcohol containing an amide group (e.g., coco mono-ethanolamide or CMEA).
The problem, however, is that it is very difficult to drive the oxidation of alcohol to carboxylic acid efficiently. The reaction will often stop at the aldehyde stage, and the yields of carboxylic acid as final products are quite low.
Japanese Patent Laid-Open No. 05/194,334 (Sandoz) discloses a process in which a hydroxyl containing compound (which may be, for example, alkyl amide polyoxyalkanol) is made to react with at least an equimolar amount of inorganic or organic halogen-containing oxidizing agent, e.g. NaOCl, in the presence of weak base and a catalytic amount of hindered nitroxide as exemplified by 2,2,6,6-tetramethylpiperidine 1-oxyl, hereafter abbreviated TEMPO, and chemical derivatives thereof. In this patent, no yield or purity information is given. The process disclosed is limited to alcohols which have polyethylene glycol or polypropylene glycol substitution, or to polyglucosides, as starting reactants. Such compounds are water-soluble or water-dispersible, which makes possible the use of water as the solvent. The patent does not teach a process using hydrophobic primary alcohols (i.e., amido alcohols) of the invention as starting reactant.
Japanese Patent Laid Open No. 04/283,537 (Shell) discloses a process using an oxidizing agent such as sodium hypochlorite in the presence of TEMPO. The process relates to production of an alkoxyalkanoic acid from the corresponding alkoxyalkanol, however, and not to the production of an amidecarboxylic acid from an alcohol having an amide group.
Japanese Laid Open No. 10/087,554 (Lion Corporation) discloses a process for production of amidocarboxylic acid from alcohol having an amide group using an oxidizing agent of chlorine type (e.g. NaOCl) in the presence of a nitroxide radical (e.g., TEMPO) and further in the presence of alkali metal halide or alkali earth metal halide (e.g., potassium chloride). In Examples 3 and 5, for example, an alcohol comprising amide; a nitroxide radical; and a 10% solution of alkali metal chloride (potassium or sodium bromide) in water, additional water, and acetonitrile (solvent) are charged into a beaker and stirred. Under these conditions, the acetonitrile and water mix together to form a single liquid phase. In each example, the purity of the carboxylic acid is calculated from the acid value, but nothing is stated about yield. The acid value is not selective for the desired carboxylic acid, but would include all acid components present,
Unexpectedly, applicants have now found that the type of solvent or solvents used during the oxidation reaction is critical to the yield of product (carboxylic acid). Without wishing to be bound by theory, applicants believe the starting amidoalcohol must not be in the same phase as the oxidizing agent. Applicants have found that this separation of oxidizing agent and alcohol can be accomplished in at least two different ways. According to a separate application applicants have filed on same date as the subject application, the final product (e.g., amidocarboxylic acid) is partitioned into an organic solvent (i.e., using solvent that will form both a hydrophobic liquid phase and an aqueous liquid phase, rather than forming one substantially aqueous phase). In this manner, the exposed amide group on the amidoalcohol is protected from cleavage (e.g., the bleach which has partitioned mainly into aqueous phase will not attack the amidoalcohol in the separate phase), and consequently far greater yield of amidocarboxylic acid is produced. That is, it is important that, in the presence of the oxidizing agent, both a solvent rich layer (substantially free of oxidizing agent) and an aqueous layer (comprising substantially of the oxidizing agent) form.
In a second embodiment, which is claimed in the subject application, the oxidizing agent and the alcohol are also maintained in separate phases. Here, however, the two phases are a water phase and a solid phase, and water alone is used as the solvent. That is, the amidoalcohol, which is hydrophobic, does not dissolve or disperse into the aqueous phase (rather it stays in the solid, non-aqueous phase) while the NaOCl remains in the continuous aqueous phase. In a preferred aspect of this embodiment (water as solvent), when chlorine or chlorinated molecule (e.g., NaOCl) is used as oxidizing agent, specific process steps (i.e., heating) must be used to ensure the amido nitrogen of the final carboxylic acid is not chlorinated as this would be an undesirable by-product.
As indicated, the subject application relates to processes where water is employed as solvent and, upon addition of oxidizing agent, the oxidizing agent partitions into solvent while amidoalcohol and/or amidocarboxylic acid stay in solid phase.